Immune receptor gene rearrangement is central to the generation of antibody diversity. This somatic recombination event is mediated by conserved recombination signal sequences (RSS) which are found immediately adjacent to all functional immune receptor gene segments sequenced to date. Murine D(H) gene segments are flanked by equivalent signal sequences; however recombination via the V(H) proximal RSS appears to be precluded until the J(H) proximall RSS has been utilized. The proposed experiments should define both the sequence motif(s) and the trans-acting factors which are responsible for this phenomenon. Immune receptor rearrangement has been intensely studied for the last decade. Unfortunately, virtually nothing is known about the enzymology of this process. In 1989 and 1990, two highly conserved genes were isolated, "recombinase activating genes 1 and 2" (RAG I and RAG 2), which are encoded within the same locus and which undoubtedly play a significant role in the somatic recombination of immune receptor genes. Though these genes were discovered nearly two years ago, biochemical information about these putative enzymes has yet to be reported. The baculovirus expresion system is being utilized to produce large amounts of these proteins so that biochemical, functional, and structural analyses can be performed. Ultimately, the goal of this research is to develop an in vitro recombination system to systematically study the enzymology of immune receptor rearrangement.